Vehicles which have a hybrid drive structure include an internal combustion engine and usually at least one electric motor as the second power plant. The driving torque may thus be generated by both power plants during operation of the hybrid vehicle. The electric drive is connected to an energy storage which supplies the electric drive with electrical energy. When the internal combustion engine is in recuperation mode, the electric drive operates in generator mode, thereby supplying the energy storage with energy. As a result, the energy storage is recharged with energy.
A high voltage, which is provided by a high voltage battery designed as an energy storage, is required for operating the electric drive. A low voltage energy system is supplied with energy from the high voltage energy system via a DC/DC converter.
In the latest developments, a starter is omitted in the manufacture of the hybrid vehicle, and the internal combustion engine is started with the aid of the electric machine.
The high voltage energy system of the hybrid vehicle is monitored at all times not only for the state of charge of the high voltage battery but also to determine whether a mechanical cover of the high voltage energy system is moved or opened. If this is the case, the high voltage energy system is immediately disconnected for safety reasons to prevent possible sparkover or to protect an operator while manipulating the energy system. Consequently, the electric machine is no longer supplied with high voltage, and the high voltage battery may no longer be recharged. Over time, this drains the battery of the low voltage energy system, which supplies the control units of the hybrid vehicle with energy. If energy is not supplied to the control units, the hybrid vehicle may no longer be operable after a certain amount of time.